1. Field of the Invention
The present invention relates to rotating closures for the discharge or runout opening in the base of a metallurgical vessel and, more particularly, to rotating closures which prevent entry of gases which may react with a melt.
2. Description of the Related Art
Rotating closures for covering the discharge opening in a base of a metallurgical vessel are well-known. For example, German Patent No. DE 42 31 692 C1 discloses a rotating closure having a stationary drain block positioned at the base of the metallurgical vessel and a runout sleeve having an inclined channel positioned within the drain block. An outlet is positioned opposite the stationary drain block and is rotatable about a vertical axis. A sleeve is inserted in this outlet, the shape of this sleeve being a mirror-inverted image of the runout sleeve. The runout sleeve and the sleeve of the outlet are in contact with each other at respective facing flat sides, i.e. in the region of their planar sealing surfaces. By rotating the outlet relative to the drain block, the through-openings, i.e. the mouths of both the channel of the drain sleeve and the sleeve of the outlet, can be made to more or less coincide in order to achieve various open positions for regulating the melt runout from the metallurgical vessel or can be held so as to be completely offset relative to one another in a closed position. The drain block, the two sleeves and the outlet are produced from conventional refractory materials. The rotation of the rotating closure is controlled by a motor, e.g. an electrical motor, via a gear unit.
In this prior art rotating closure, the two sleeves can be subject to sharply different degrees of heating during operation due to the inclined channel causing one-sided warping of the sleeves thus affecting the tightness of the sleeves in the region of the contact surfaces. A further disadvantage is that the high flow rates in the channel of the upper region of the rotating closure due to the cross sectional area of the channel generate a strong vacuum pressure causing air to be sucked in from the environment through the porous refractory material and to come into contact with the melt. This, in turn, often brings about unacceptable oxide formations in the melt. In order to prevent this, it is known to shield the rotating closure using a protective-gas shrouding. However, the use of such a protective-gas shrouding is very expensive.
It is thus desirable to provide a rotating closure which is able to effectively prevent the entry of gases which would react with the melt in a cost efficient manner.